In a variety of marine environments, seismic surveys are conducted to gain a better understanding of geological formations beneath a body of water. Relatively large marine regions can be surveyed by a surface vessel or vessels towing seismic streamer cables through the water. Another vessel, or the same vessel, can be employed in providing seismic sources, such as compressed air guns utilized to generate acoustic pulses in the water. The seismic sources can be arranged in source arrays. In some applications, for example, air guns are suspended from a float and towed behind a seismic vessel. During towing, however, drag forces on the source array deform the shape of the array which can be detrimental to obtaining accurate seismic data.
Currently, a common technique for creating seismic source arrays is to position all the guns at one layer and to suspend the guns from a float. A tow rope extending from the towing vessel is coupled directly to the gun array. In other applications, the tow rope is connected directly to the float or float layer. In either application, the source array deforms substantially during towing.
Attempts also have been made to construct source arrays with the guns arranged in layers separated vertically. However, the towing of multilayered gun arrays tends to be far more complex than towing a single gun layer. Depending on how towing ropes and distance ropes are arranged, the shape of the source array can be severely distorted during towing relative to its nominal position. The towing shape is substantially altered due to the drag forces exerted by the water against the source array.